Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $67.93   13.223%   $76.9124   $76.91   $76.90   $76.90  
  Purchase #2 $162.40   8.569%   $176.3161   $176.32   $176.30   $176.30  
  Purchase #3 $212.36   3.124%   $218.9941   $218.99   $219.00   $219.00  
  Purchase #4 $55.32   13.364%   $62.713   $62.71   $62.70   $62.70  
  Purchase #5 $182.82   4.775%   $191.5497   $191.55   $191.55   $191.50  
  Purchase #6 $51.29   8.751%   $55.7784   $55.78   $55.80   $55.80  
  Purchase #7 $214.43   5.216%   $225.6147   $225.61   $225.60   $225.60  
  7 purchase totals = $946.55       $1,007.8784   $1,007.87   $1,007.85   $1,007.80